1. Field of the Invention
The present invention relates to a distributed-memory multiprocessor system in which a plurality of nodes are mutually connected by a network and in particular, to a method for controlling an inter-node communication and a task scheduling operation on the distributed-memory multiprocessor system.
2. Description of the Prior Art
In order to effectively execute parallel-distributed programs of which each composed of a plurality of tasks on a multiprocessor system composed of a plurality of nodes, it is important to schedule a plurality of tasks that belong to the same application at the same time. As an example of such a scheduling method, the gang scheduling method is known.
However, the gang scheduling method was designed for a memory-shared multiprocessor system. Thus, in a distributed-memory multiprocessor system in which sharing information among processors costs a lot of time, the communication cost for sharing information should be decreased so as to reduce the overhead of the scheduling operation.
On the other hand, in order to enhance the performance of an inter-node communication for user tasks, there has been used an inter-node communicating system that operates in the user level and therefore that does not require a system call of an OS (Operating System). Such user-level communicating method and the gang scheduling method may be used in combination.
However, a user-level communication takes place in the level which does not concern OS. In addition, in a conventional user-level communication, each node has a single reception buffer. Thus, when one task is switched to another task (that is to say, a context switching operation is performed), in order to assure that communication data does not exist on the network and on the reception buffer, after one user task is stopped, it is necessary to confirm that no packet exists on the network and to save the reception buffer. Thus, such operations result in a large overhead.
Consequently, the context switching operation for user tasks in the gang scheduling method takes a long time. In order to suppress the influence of the lone time necessary for the context switching operation, the intervals of the context switching operation may be prolonged. However, in this case, the response characteristic of an interactive process with the user becomes deteriorative.
Thus, it takes a long time to perform the context switching operation in the distributed-memory multiprocessor system when the context switching operation employs the user-level communication. Consequently, the response characteristic and throughput of the system become deteriorative.